The main interface to a transport that creates a Channel associated
with a certain communication entity such as a network socket. For example,
the NioServerSocketChannelFactory creates a channel which has a
NIO-based server socket as its underlying communication entity.

releaseExternalResources

void releaseExternalResources()

Releases the external resources that this factory depends on to function.
An external resource is a resource that this factory didn't create by
itself. For example, Executors that you specified in the factory
constructor are external resources. You can call this method to release
all external resources conveniently when the resources are not used by
this factory or any other part of your application. An unexpected
behavior will be resulted in if the resources are released when there's
an open channel which is managed by this factory.